This invention relates generally to testing methods and systems for determining motor performance parameters and, more particularly, to a system and method for testing and collecting data relating to performance of thermal protector devices for electric motors.
Electric induction motors typically include motor windings housed in a stator assembly within a motor shell. As the windings are energized, a voltage is induced in a rotor inserted within the stator, and a resultant magnetic field causes the rotor to rotate within the stator and power devices attached to a rotor shaft that extends from, and rotates with, the rotor. A thermal protector device is typically connected between a motor power supply and the motor windings to protect against excessive heat buildup in the windings as current flows through the windings.
As current flows through the motor windings and heats the windings, current also flows through the thermal protector device and heats the device. When the thermal protector device reaches a pre-determined temperature, the device opens or xe2x80x9ctripsxe2x80x9d and disconnects the windings from the motor circuit to prevent damage to the motor. As the thermal protector device cools, it eventually closes or xe2x80x9cresetsxe2x80x9d and completes the motor circuit to energize the windings. As current flows through the thermal device and windings, heat generated by the current flowing through the device causes the thermal protector to trip and again open the circuit, and as the thermal protector device cools it again resets and closes the circuit. Hence the thermal protector device cycles motor power on and off to prevent overheating of the motor in use.
To ensure customer satisfaction, motor performance, and motor reliability, a number of motor characteristics are typically tested before motors are delivered to customers to determine whether the motor meets certain specifications, including but not limited to UL (Underwriter""s Laboratory) certification standards. At least one UL standard relates to thermal protector devices for motors, and entails recording of the first five xe2x80x9conxe2x80x9d or reset times and the first five xe2x80x9coffxe2x80x9d or trip times of a motor power cycle through the thermal protector device in use. Conventionally, timing of power cycles has been accomplished with complicated electromechanical systems including ten electromechanical timers for display to an operator for recording the five reset and five trip power cycles of the motor. Electromechanical timers are very expensive, in short supply, and require some effort to maintain and ensure the reliability of system measurements.
Accordingly, it would be desirable to provide a lower cost and less complicated system and method for collecting data relating to the operation of a thermal protector device for a motor.
In an exemplary embodiment of the invention, a system is provided for testing thermal protector device performance in a motor including a motor winding and a thermal protector device coupled thereto that cycles between a reset or xe2x80x9conxe2x80x9d position and a trip or xe2x80x9coffxe2x80x9d position to cycle power to the motor winding and prevent motor damage from overheating of the motor winding. The system includes a microprocessor configured to measure elapsed times of reset and trip power cycles of the motor winding through the thermal protector device, a memory for storing and recalling the elapsed reset and trip times, and an operator interface terminal coupled to the microprocessor. The operator interface terminal includes a display and at least one input selector for displaying the elapsed reset and trip times in response to user manipulation of the input selector.
More specifically, the microprocessor is configured to measure and store a pre-determined number of thermal protector device reset and trip times in the memory, such as, for example, the five reset and trip times required by UL standards.
After the predetermined number of reset and trip times are stored in the memory, the microprocessor is configured to store and display a last timed power cycle of the motor winding, as well as a total number of timed power cycles of the motor winding through the thermal protector device. A current sensor is coupled to the microprocessor and configured for coupling to the motor in series with the thermal protector. The current sensor provides a signal to the microprocessor that triggers measuring the elapsed reset times and the elapsed trip times of the thermal protector device.
Therefore, a lower cost, less complicated and user-friendly system is provided for collecting data relating to the operation of a thermal protector device for a motor.